Burner and combustion system



Feb. 14, 1956 R, L, HARRIS RT AL 2,734,560

BURNER AND COMBUSTION SYSTEM Filed Oct. 9. 1951 WSNQA :EIS- z I N V ENTOR. BERT L, HARK/5 MARCUS G77/POP United States Patent O BURNER ANDCOMBUSTION SYSTEM Robert L. Harris and Marcus Lothrop, Berkeley, Calif.,

assignors to Yuba Manufacturing Company, San Francisco, Calif., acorporation of California Application October 9, 1951, Serial No.250,452

4 Claims. (Cl. 158-4) Our invention relates to apparatus primarily foruse in connection with mobile steam power plants and ofl a type usefulin connection with a steam generator as disclosed in our co-pendingapplication Serial No. 28,548, now Patent No. 2,645,210, issued July 14,1953, tiled May 22, 1948, and utilizing a fuel burner system of the sortdisclosed in our co-pending application Serial No. 27,374, tiled May 17,1948, now Patent No. 2,589,224, issued February 19, 1952.

In mobile power plants of the type indicated, it is desirable to havespark ignition of the fuel for combustion and to have the lire operateintermittently and also to vary substantially in quantity from a Verysmall amount to a very large amount. While the ignition of the lireinitially at a relatively low rate when the structure is being startedfrom cold is readily accomplished by the usual spark ignition device, itis sometimes difcult, even after the structure has been operating forsome time, to ignite a very large quantity of fuel Asuddenly dischargedinto the combustion system. lt has also been found that to providesatisfactory relatively smoke free and efficient combustion over a verywide range, for example a range of eight to one, is diiicult in a singlecombustion chamber. That is, it is easy to design a combustion chamberwhich operates well with a given amount of fuel but it is not easy toarrange a structure which operates well with greatly differentquantities of fuel.

Despite the availability of materials resistant to relatively hightemperatures, it is difficult to afford a combustion chamber having arelatively long life in an environment in which a very large quantity offuel is burned in a relatively small volume.

It is therefore an object of our invention to provide a burner andcombustion system effective to burn a relatively small quantity or arelatively large quantity of fuel in substantially the same combustionchamber.

Another object of our invention is to provide a burner and combustionsystem in which ignition of an intermittently operating flame issuccessful at very large volumes of fuel.

Another object of our invention is to provide a burner and combustionsystem effective over a long period of ytime without substantialdeterioration even though the quantity of fuel burned varies rapidly andsomewhat at random from a relatively small amount toa relatively greatamount.

A still further object of our invention is in general to improve burnerand combustion systems.

A still further object of the invention is to provide a burner andcombustion system which utilizes ordinary materials and simplestructures to produce a satisfactory combustion, particularly asatisfactory intermittent combustion over a very wide range ofquantities.

Other objects, together with the foregoing, are at tained in theembodiment of the invention described in the accompanying descriptionand illustrated in the accompanying drawing, in which:

Figure l is a cross `section o nAa longitudinal vertical 2,734,560Patented Feb. 14, 1956 ICC plane through a burner and combustion systemconstructed in accordance with our invention and illustrated in partdiagrammatically.

Figure 2 is a detail shown in cross section on the line 2 2 of Figure l.

Figure 3 is a detail shown in cross section on the line 3-3 of Figure l.

While the burner and combustion system is susceptible to wide variationdepending upon numerous design factors and particularly upon theassociated mechanism with which it is to operate, it has successfullybeen embodied as illustrated herein in connection with a steam generator6, within which is disposed a circular cylindrical cornbustion tube 7,having a central axis 8. The tube is preferably fabricated of combustionresistant metal or other suitable material. The combustion tube 7adjacent one end is spaced from the wall 9 of the generator to leave anintervening annular air inlet opening 10 connected to suitable source ofcombustion air under pressure such as a blower, not shown.

Spanning the end of the combustion tube 7 and removably fastened to thewall 9 is a face plate 11 serving as a support for additional structure.The face plate is preferably made up of an outer ring 12 of light metaljoined to a dished plate 13 itself connected to an outer cone 14truncated and spanned by a disc 16, the plane of which is somewhatbeyond the general plane of the ring 12. The dished and conical contourof the face plate 1l is to avoid severe warpage under intermittent hightemperature. Y

The disc 16 is symmetrical with the axis 8, being perpendicular thereto,and is effective to carry a burner plate 17 on which a main burnernozzle 18 and an auxiliary burner nozzle 19 are mounted. Upon removal ofthe plate 17 the two nozzles can be removed, but when the plate is inposition the axes of the nozzles are substantially parallel to the axis8 and are as close to it as is mechanically feasible. The main nozzle 18is connected by a conduit 2 through a control valve 22 to a supplyconduit 23 leading to any suitable source of fuel oil. An additionalcontrol valve 24 not only controls the principal supply of oil to themain nozzle 18 but likewise controls supply through a conduit 26 to theauxiliary nozzle 19.

The nozzles i8 and 19 discharge hollow cones of fuel spray approximatelyindicated by envelope lines 27 and 28. This showing is at best anapproximation as the envelope is not sharply dened and also varies underdifferent operating conditions, but is intended to afford asubstantially correct showing. The envelope lines 27 extend in thegeneral direction of the axis 8 diverging as they proceed away from thenozzle 18 and do not intersect or interfere with the envelope lines 23of the nozzle 19 until a substantial axial distance has been traversed,although at a greater distance the two envelopes approximately mergeinto quite similar patterns.

The envelope lines 28 of the spray cone from the nozzle i9 areapproximately intercepted by the electrodes 3l of a spark igniter 32.This is conveniently a standard automobile type grounded sparkplug'screwed into an appropriate boss 33 in the outer cone 14 andprovided with an ignition lead 34 in the usual way. The location of theelectrodes 3l is adjacent the auxiliary nozzle 19 but remote lfrom themain nozzle 18,

Situated coaxially within the tube 7 is a combustion cone 36, preferablyfabricated of relatively inexpensive sheet metal. This is feasible sincethe outer portion of the combustion cone 36 is subjected to and keptfrom excessive temperature by substantially all of the relatively coolcombustion air entering through the passageway 10. The cone 36 isarranged with its small end adjacent the nozzles 18 and 19 and in somecases is actually fastened to the disc 16,.v and in other cases isdisposed inclose proximity thereto. Cut out. portions 37 are providedinthe combustion cone not only to avoid mechanical interference with thenozzles 18 and 19 but likewise to admit some air in the immediatevicinity of the nozzles although the cut out portions are protected froma direct blast of entering air by the truncated outer cone The angle ofdivergence of the combustion cone 36 is somewhat greater than the angleof divergence of the spray envelopes 27 and 28. The larger end of thecombustion cone terminates in an annular pocket 4l defined in part andon the outside by the combustion tube 7 and in part and on the inside bya dellector cone 42, preferably fabricated also of sheet metal andprovided with a rim flange 42 having, if desired7 an inturned portion 44in rather close engagement with the combustion tube 7. Preferably thecombustion cone 42 has a frictional sliding fit within the combustiontube 7 in order to preclude the passage of any substantial amount ofcombustion air around the deilector cone. In some instances, the flange43 is either a sufficiently loose it within the combustion tube '7 or isactually cut away or apertured to permit some of the combustion air topass by the deflector cone 452.

In the preferred instance as shown, the size of the pocket 41 is suchand the dimensions of the detlecting cone 42 are such that the smallerend of the deflector cone is nested within the larger end of thecombustion cone 36. Both cones are well outside the fuel sprayenvelopes. There is an axial amount of overlap to define an annularpassage 46 between the two cones. This passage is shaped to be effectiveto control the direction of flow of air. Incoming air, indicated byarrows i7 flows generally radially inward from the opening il) and inmost instances is also possessed of some rotational swirl about the axisti as a center, either due to the operation of the blower mechanism ordue to the provision of auxiliary swirl vanes in the opening 10, or dueto unavoidably unsymmetrical flow.

In any case, the inowing air following the path 47 travelling into thepocket di reverses its direction in flowing through the opening 46 sothat it has a substantial component of flow opposite to the direction offlow of fuel from the nozzles 18 and 19. This is believed to beimportant as it produces a large relative travel between the fuel andthe air to assist in obtaining a maximum admixture.

It has been observed in practice that air passing through the passageway46 and entering the combustion cone 36 is possessed of sutcientasymmetry to have a swirl component and. forms a vortex within the coneSe. it is bclieved that ideally it would be possible to introduce airinto the large end of the combustion cone 36 without any vorticalmotion. But in practice there seems always to be swirl, and it seems notto be necessary to provide specific swirl inducing means. However, forpurposes of iliustration herein and for convenience ink fabrication andto insure that a large amount of swirl of a vortical nature is provided,the passage 46 is spanned by a number of small vanes 4S, interposedbetween and in most instances fastened to the combustion cone 36 anddeliector cone 46.

The air stream has a vortical swirl as it discharges from between thevanes 48 and as it travels in a direction toward the left in Figure lalong the axis 3 and around the inside of the combustion cone 36. Theswirling air encounters smaller and smaller cone diameters as itapproaches the burner nozzles. The rate of rotational velocity of thevortical air swirl increases very marlrediy, and the violencev of therotary air movement increases greatly toward the small end of thecombustion cone 5-3.

While the countercurrent direction of motion is helpful and while theviolent vortical motion is productive of excellent combustion, in theregion of the large part of the combustion cone and,V of the deliectorcone i2 and even withinthe combustion tube 7 toward the right in Figurel, it hasbeen determined that such vertical swirl is entirelyr too:violent andi acts too much as a centrifugal separator in the small endofY the, combustion cone. 3.6 near the nozzles. The centrifugal forceinstead of merely providing desirable turbulence apparently tends toform concentric zones of material too rich for combustion and too poorfor combustion. It has been noted that the violent swirl tends todisrupt the fuel envelopes and in many instances interferessubstantially with ignition.

Consequently, adjacent the srnall end of the combustion cone 36 near theburner nozzles 18 and 19 and in the vicinity of the spark plugelectrodes 31, and also in a region where the spray envelopes 27 and 28andy have not yet merged, there are disposed a number' of arrestingvanes 49. These are strips of metal secured to the combustion cone 36extending in the general direction of the axis S and also extending asubstantial amount radially toward the center of the cone. They arepreferably disposed so a" not to interfere with but rather to shield theelectrodes 3': and so as not to intercept any of the liquid spray fromthe nozzles lf3 and 19. The vanes 49 have the effect, in generai, ofpreventing rapid swirls about the axis t5 in the small end of thecombustion cone 36 and afford what relatively a quiescent zone. Thereare some eddies and turbulence in the vicinity of the arresting vanes49, but in part they come also from air entering through the relievedportions 37.

To initiate operation of this structure, the spark plug 32 is energizedin the usual way and a continuous spark is afforded at the electrodes3i. The control valve 24 is suitably opened but the valve 22 remainsclosed. There is a flow of fuel through the conduit 26 to the auxiliarynozzle 19. in one representative instance this nozzle has a capacity ofspraying one gallon of fuel per hour, a relatively minor amount'of oil.The small quantity of fuel emerging from the auxiliary nozzle i9 hasntmuch penetration and is relatively protected within the small end of thecombustion cone 36, a sort of protected cove, despite tne fact thatcombustion air in quite large quantity is entering through the openingor annulus l0. Most of the combustion air passing rather violentlythrough the swirl vanes 4o, reverses itself and passes then through theinterior of the deflector cone 42 into the combustion tube 7 toward theright in Figure l. Only some mildly turbulent air passes the arrestingvanes 49 and may be augmented by a small amount of low velocity airentering through the cutaway portions 37. The relatively quiescentconditions in the small end of the combustion cone facilitate theimmediate spark ignition of the relatively small quantity of vaporizedfuel within the envelope 23. A moderately small flame then burns withinthe combustion cone 36, mostly in the small end thereof, and theproducts of combustion mix with the main portion of air traveling intothe combustion tube '7.

Simultaneously with or preferably slightly after the primary ignitionhas taken place, the valve 22 is opened and a larger supply of oilissues from the main nozzle fre. This quantity of oil, in arepresentative instance, ranges from say four gallons per hour to saythirty two gallons per hour, Occasionally, nozzles in addition to thenozzles 18 are utilized, several at a time being out into or out ofoperation simultaneously or sequentially but for illustration herein thenozzle 18 represents a variable main fuel supply. This main supplyenters the smail end of the combustion cone 36 and does not immediatelymix with the supply from the auxiliary nozzle.

The main supply need not be directly ignited by the spark plug 3l sincethe electrodes are relatively far away and the proportions of the airzuid fuel may not be appropriate, although sometimes direct ignitionappears to occur. ln any case, there is luminous combustion or flamefrom the auxiliary nozzle in the vicinity of the mid point of thecombustion cone 36 and somewhere in that zone the fuel from the mainnozzle, as represented by the envelope 27, is mixed into the auxiliaryllame. Ignitionof the main quantity of fuel therefore, is designed totake place from the auxiliary llame rather than directly Y from thespark plug itself. l Y

As the main quantity of fuel travels toward the right in Figure 1 itencounters a very violent vortical swirl of air having a substantialcomponent toward the left in Figure l. The resulting turbulence admixesthe air and oil in a very short space of travel and in a relativelysmall chamber volume. Combustion of the entire quantity thereupon ensuespartly in the combustion cone and partly as the mixture travels from theinterior of the deflecting cone 32 out into the combustion tube 7. Thistube is relatively long and combustion isentirely completed within it. f

The operation of the main nozzle 18 is interrupted quite abruptly fromtime to time by closure of the valve 22 although the supply of airthrough the opening 10 may not be changed at all. If the proportions ofair and oil are proper for combustion before the interruption ofoperation of the main nozzle 18, they are improper after the fuel hasbeen interrupted. However, the auxiliary nozzle is Well enough protectedfrom the main -air rflow so that its combustion continues properlywithout interruption. When the mainV nozzle 18 is again effective, uponabrupt opening of the valve 22 to discharge oil at the rate of saythirty-two gallons an hour into the combustion cone 36 (whichimmediately theretofore has been supporting combustion at the rate ofonly one gallon per hour), the ignition of this large quantity ofrelatively cold fuel nevertheless is positive and immediate because theauxiliary flame is suiiicient to insure that result, and suicient air isavailable toward the larger portion of the combustion cone.

The description of combustion events and locations is as accurate aspossible but due to diculty or observation in practice onlyapproximations can be given.

We claim:

l. Av burner and combustion system comprising a smooth substantiallyimperforate combustion cone having an axis, a nozzle disposed at thesmall end of said combustion cone and directed in a predetermineddirection along said axis `toward the large end of said combustion cone,means for directing an air stream into the large end of said combustioncone in an opposite direction and toward the small end of saidcombustion cone, means adjacent the large end of said combustion conefor imparting to said air stream a vortical swirl about said axis andalong the inner surface of said cone, and means only adjacent the smallend of said combustion cone and axially between said nozzles and thelarge end said cone for arresting said vortical swirl only in thevicinity of the small end of said combustion cone.

2. A burner and combustion system comprising a smooth combustion conehaving an axis, a nozzle disposed at the small end of said combustioncone and directed along said axis toward the large end of saidlcombustion cone, ardetector cone nested within the large end only ofsaid combustion cone to leave an annular opening therebetween, swirlvanes spanning said opening for imparting a single unidirectional swirlabout said 6 axis to air owing through said opening along the inside ofsaid combustion cone toward the small end thereof,

and axially disposed arresting vanes within the small lend only of saidcombustion cone. and located axially between said nozzle and saidannular opening for arresting said unidirectional swirl adjacentthesmall end only of said combustion cone.

3. A burner and combustion system comprising a combustion cone having anaxis, a pair of nozzles directed into the small end of said combustioncone to discharge spray in a predetermined direction along said axistoward the large end of said combustion cone, a spark igniter projectinginto said combustion cone in a position to ignite said spray from one ofsaid nozzles, means for directing an air stream into the large end ofsaid combustion cone in a direction opposite to said predetermineddirection, means within the large end of said combustion cone forinducing a single unidirectional swirl of said air stream within saidcombustion cone and owing along the inner wall thereof toward saidnozzles, and means for arresting said swirl of said air stream withinsaid combustion cone but'only adjacent the small end thereof on thespray side of said nozzles.

4. A burner and combustion system comprising a substantially smoothcombustion cone symmetrical about an axis and having a small end and alarge end, a fuel nozzle disposed adjacent said small end and effectiveto discharge fuel in a conical stream along said axis toward said largeend, a deector cone symmetrical about said axis and telescoped withinthe large end of said combustion cone to provide'an axial overlap of aportion of the large end of said combustion cone and a portion of thesmall end of said deflector cone, said portions being radially spacedapart to leave a passageway therebetween, a single set of vanes in saidpassageway for imparting a .unidirectional swirl to air owing throughsaid passageway toward said small end of said combustion cone and fordischarging saidair with a unidirectional swirl onto said smoothcombustion cone with an axial ilow component toward said small end ofsaid smooth combustion cone, and swirl arresting vanes within saidcombustion cone only in said small end thereof adjacent the fueldischarge side of said fuel nozzle for arresting said swirl of only thatportion of said air adjacent the fuel discharge side of said nozzle.

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